High-temperature stable electro-conductive aluminum-base alloy

ABSTRACT

An aluminum-base alloy contains components at the following ratio of the same, in mass %: copper 0.5-2.0; manganese 0.3-1.6; zirconium 0.1-0.5; boron 0.02-0.15; silver 0.01-0.5; scandium 0.02-0.15; iron 0.01-0.3; silicon 0.01-0.35; inevitable admixtures 0-0.1 each one of them with 0-0.03, the remnant being aluminum. At the same time, boron, zirconium and scandium are present as nanoparticles AlB 2 , AlB 12  borides and Al 3 (ZrSc) with an average size of no more than 50 nm to provide electric conductivity of at least 55% IACS, the ultimate strength (σ β ) after exposure to 250° C. for 400 hours being at least 170 MPa. The alloy shows increased thermostability and electric conductivity and is foreseen for items operating under elevated temperatures.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority from Russian Patent Application No. 2014127784 filed Jul. 8, 2014, which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to metallurgy and more particularly to deformable nanostructured alloys on the basis of aluminum, copper, manganese, zirconium, scandium, iron, silicon and to a process of their manufacture for products operating under elevated temperatures. In particular, the alloy can be used in aviation, astronautics, automobile manufacture in items for electrical engineering where a combination of rather high strength, heat-resistance and electric conductivity is required.

BACKGROUND OF THE INVENTION

There are known alloys of the system Al—Cu—Mn with a high copper content (Mashinostroyenie. Encyclopedia in 40 v., volume 11-3. Non-ferrous metals and alloys. Moscow. Mashinostroyenie, 2001, p. 144-156). These are alloys D20, 1201, D21, 01205 with 5.8-7.0 mass % of copper. They show electric conductivity of no more than 30-35% IACS.

It is known an alloy of the patent RU2287600 published on 20 Nov. 2006, containing copper, manganese, zirconium and vanadium, comprising an aluminum solid solution and secondary aluminides, characterized in that it additionally contains scandium at the following component ratio, in mass %: copper 1.2-2.4; manganese 1.2-2.2; zirconium 0.5-0.6; vanadium 0.01-0.15; scandium 0.01-0.2; the rest being aluminum. After 100 hours of seasoning, the alloy has the ultimate strength of more than 30 MPa at 350° C. For a rather high ultimate strength of 300 MPa after 1-20 minutes of annealing at 200-410° C., the alloy shows a low electric conductivity that is lower than 48% IACS.

The closest prior art of the present invention is an alloy on the basis of aluminum (patent RU2446222, published on 27 Mar. 2012), containing the following component ratio in mass %: copper 0.9-1.9; manganese 1.0-1.8; zirconium 0.2-0.64; scandium 0.01-0.12; iron 0.15-0.5; silicon 0.05-0.15; the rest being aluminum; the nanoparticles of the phase Al₃(Zr, Sc) with the average size of no more than 20 nm, electric conductivity is higher than 53% IACS, the ultimate strength σ_(β) after 100 hours at 300° C. is higher than 320 MPa.

A drawback of said alloy, in spite of many advantages, is in its low strength at the temperature of 250° C. and after seasoning during 400 hours, as well as in its electric conductivity (53% IACS).

SUMMARY OF THE INVENTION

The present invention has the task to create a new nanostructured deformable aluminum-base alloy that shows a higher thermal resistance and/or electric conductivity compared to the closest prior art alloy for various semifinished products and finished items.

DETAILED DESCRIPTION

The task assigned is solved thanks to the fact that a heat-resistant conducting aluminum-base alloy containing copper, manganese, zirconium, scandium, iron and silicon, an aluminum solid solution and secondary manganese, zirconium and scandium aluminides, according to the invention, additionally comprises silver and boron for a lower copper content, with the following component ratio in mass %:

-   -   copper 0.5-2.0     -   manganese 0.3-1.6     -   boron 0.02-0.15     -   silver 0.01-0.5     -   zirconium 0.1-0.5     -   scandium 0.02-0.15     -   iron 0.01-0.30     -   silicon 0.1-0.35     -   inevitable admixtures 0-0.1, each one of them with 0-0.03,     -   the rest being aluminum.

In this case, boron, zirconium, scandium are present in the structure as nanoparticles with an average size of no more than 50 nm, of AlB₂, AlB₁₂ borides (including inevitable admixtures) and of Al₃ (Zr, Sc) to provide electric conductivity of at least 55% IACS and the ultimate strength (σ_(β)) of at least 170 MPa after 400 hours of heating at 250° C.

In this case, boron forms stable segregations in near the areas on the crystal lattice defects, which improves the alloy ability to deformation and modifies the ageing kinetics. For a more stable increase of heat-resistance, the alloy can additionally contain in mass %: cobalt 0.1-0.45 and/or nickel 0.1-0.35, and/or cadmium 0.1-0.3, and/or P3M 0.001-0.1, and/or germanium 0.05-0.3.

The alloy can be produced as various cast and deformed semifinished products (sheets, bars, stamped parts, wire for conductors aboard and for other applications) the manufacturing technology of which comprises the operation of making a melt at a temperature exceeding by 100° C. the liquidus temperature. The components are added to the melt as master alloys with a finely crystalline structure, at an average nanoparticle size of no more than 1300 nm In the case of using a master alloy Al—B—Ti or Al—Cu—Mn(Ti), the titanium content in the melt is kept at a ratio of no more than 0.03 mass %.

Furthermore, the crystallization of a cast blank and the deformation of the same are carried out under the effect of a magnetic pulse field and/or a low-pulse current to provide a necessary size of nanoparticles and a required heat-resistance.

To provide a cast structure closer in properties to a deformable one, high temperatures of 900-800° C. are maintained during crystallization.

Manganese, zirconium and cobalt slow down the solid solution dissociation at high temperatures and slow down the recrystallization process. Manganese and copper used in mentioned concentrations lead to the formation of dispersoids providing for the main requirements of strength and thermal conductivity, while increasing the same leads to reduce electric conductivity. Zirconium and scandium favor nanoparticle formation and contribute to provide for a required strength at elevated temperatures. An increase of their content reduces electric conductivity. Small concentrations of manganese increase long-term strength at temperatures 250-300° C.

Iron and silicon reduce electric conductivity as well, but when under combined compounds with manganese of the eutectic type Al(Fe, Mn) Si, they favor formation of a structure increasing the allow strength.

Boron used as nanoparticles with aluminum and as borides with transition metals increases the alloy electric conductivity. At the same time, boron forms stable segregates in boundary areas on defects of a crystalline lattice, it increases the ability of the alloy to deformations and, at some extent, it speeds up the ageing kinetics.

Examples of Making the Claimed Material

Alloys were made in an electric resistance furnace with alundum crucibles at a melt temperature exceeding by 100° C. the liquidus temperature. As a melting stock, use was made of aluminum (99.9%), copper (99.9%) and fine-grained alloying compositions: double Al—Mn, Al—Zn, Al—Sc, Al—Si, Al—Fe, ternary alloying compositions Al—B—Ti and/or Al—Cu—Mn (Ti). The compositions of alloys are given in Table 1. Round ingots were cast into a cylindrical mould. The magnetic-pulse fields (MPF) were used to stir the melt, and the low-pulse current was used in the crystallization process.

Then specimens were annealed at 450° C.±10° for 4 hours and upset to 60-70%, their Brinell hardness and electric conductivity were measured. The electric conductivity was determined by the eddy current method.

As on can see from an analysis of Table 1 and 2, the compositions No 1 and No 2 are characterized by a higher electric conductivity while the compositions 3 and 4, by a higher ultimate strength after maintaining at 250° C. for 400 hours compared to the closest prior art (RU2446222).

TABLE 1 Chemical composition of experimental alloys (in mass %) Heat Admixtures number Cu Mn Zr Fe Si Sc B Ag in sum Al 1 0.8 0.6 0.12 0.1 0.1 0.12 0.05 0.02 0.08 the rest 2 0.8 0.6 0.12 0.1 0.1 0.12 0.06 0.15 0.08 the rest 3 1.5 1.4 0.5 0.3 0.1 0.06 0.15 0.20 0.1 the rest 4 1.8 1.4 0.5 0.3 0.1 0.06 0.08 0.50 0.1 the rest

TABLE 2 Mechanical properties and electric conductivity of alloy specimens after annealing at 250° C. for 400 hours Heat number

, MPa IACS, % 1 175 57 2 202 56 3 273 55 4 310 55 RU2446222 230 53 

1. A heat-resistant conducting aluminum-base alloy comprising copper, manganese, zirconium, scandium, iron and silicon, characterized by a structure comprising an aluminum solid solution and secondary manganese, zirconium and scandium aluminides, and additionally comprising silver and boron, with the following component ratio in mass %: copper 0.5-2.0 manganese 0.3-1.6 boron 0.02-0.15 silver 0.01-0.5 zirconium 0.1-0.5 scandium 0.02-0.15 iron 0.01-0.30 silicon 0.1-0.35 inevitable admixtures 0-0.1, each one of them with 0-0.03, the rest being aluminum; wherein boron, zirconium and scandium are present in the structure as nanoparticles with an average size of no more than 50 nm of AlB₂, AlB₁₂ borides (including inevitable admixtures) and of Al₃ (Zr, Sc) to provide electric conductivity of at least 55% IACS and the ultimate strength (σ_(β)) of at least 170 MPa after 400 hours of heating at 250° C.
 2. The alloy of claim 1, further comprising one or more of the following in mass %: cobalt 0.1-0.45, nickel 0.1-0.35, cadmium 0.1-0.3, P3M 0.001-0.1, and germanium 0.05-0.3. 